Below are some general rules for correctly designing a hot runner.

The most common problem encountered is due to improper heat balance. This deficiency may be the result of many different factors. For example, external heating using wound heating elementshot runner nozzleThe problem may be that the heat transfer surface is too small, leading to complete failure of the hot runner system. When using tubular heaters, the same problem may occur without appropriate supports.

In this case, the insulation effect of the air gap between the tubular heater and the hole where the tubular heater is placed may lead to the accumulation of heat in the tubular heater on the one hand, and at least cause local unreasonable heating on the other hand, even if the heating power has been correctly determined. The accumulation of heat in a tubular heater usually leads to premature failure, which shortens the service life of the tubular heater.

It has been proven successful to embed the tubular heating element into the heat conduction adhesive placed in the rough channel of processing. Because according to the arrangement of the hot runner plate, these tubular heating elements can respectively adapt to local heating requirements, and in many cases, they can help improve heat balance.

When using reasonable process procedures, that is - to avoid air entrainment in the heat transfer adhesive - to coat the entire surface of the tubular heating element and the channel where the tubular heating element is placed with heat transfer adhesive - for treating heat transfer adhesive, the manufacturer must be followed. In this way, the operating procedures will extend the service life of the tubular heating element and reduce its sensitivity to failure.

Due to the brittleness and possibility of fragmentation of heat transfer binders, the channels of tubular heating elements must be well covered. According to the principle of heat transfer, it is best to use bright cold rolled or polished aluminum plates fixed on the hot runner plate to achieve this goal. The requirement for uniform heat balance on the hot runner plate mainly includes minimizing local temperature differences, because when the probe (torpedo body) is indirectly heated by the hot runner system, the same temperature at the tip of the probe is a necessary prerequisite. If there is no temperature fluctuation in the hot runner plate as much as possible, most of the cushion blocks should be as high as possible, heat loss should be as low as possible, and the temperature should be controllable.

In order to determine the heating capacity of the hot runner, it has been proven that the heating capacity of the hot runner plate is successful based on a ratio of 150 to 300W. Especially, it should be noted that too high a unit heating capacity (300W/ks heating capacity of the hot runner plate) can cause large and adverse temperature fluctuations in the hot runner plate. To control the temperature of the hot runner plate, it is recommended to use a quasi continuous controller that reduces power output at the beginning of operation. However, it must be taken into account that even the most sensitive temperature controller cannot correct the issue of thermal balance without simultaneously trying to minimize heat loss.

For example, in a hot runner mold with four nozzles, the result of convective heat loss caused by the flue effect is a temperature difference measured within 60 degrees. Although the hot runner system is designed correctly using other methods, it is impossible to continuously produce plastic parts according to technical requirements. Covering the open part of the mold can easily eliminate the flue effect. This measure resulted in a significant reduction in temperature difference.